Gamma-radiation apparatuses have been proposed for non-invasive neurosurgery of the brain in order to treat cerebral lesions without opening the cranium. Destruction of the lesions is achieved by precisely concentrating gamma radiation onto the areas to be treated, such as venous malformations or tumors. These apparatuses are often designated by the name "gamma surgical apparatuses" or "gamma bistouries".
In these apparatuses, external gamma-radiation sources are used, the radiation being directed and concentrated, in a precise manner, onto the treated lesion in order for the desired dose to be absorbed by this lesion without appreciably damaging the intermediate tissues intervening between the sources and the lesion, nor the tissues surrounding the lesion and, in a general manner, reducing to a minimum the radiation doses absorbed by the healthy tissues.
This is achieved especially by the devices of the aforementioned type, an example of which is described in FR-A-2,672,220. In this technology, a large number of fixed external sources are used, these being collimated individually and arranged radially so that the axes of the rays that they produce converge onto a focal point which coincides with the lesion to be treated. The intensity of each beam is insufficient to damage the intermediate healthy tissues through which it passes, especially as the device is given, during the treatment, an angular movement about the focusing point. In contrast, at the point of convergence or focal point, the dose received by the lesion is sufficient to destroy it.
In this known technique, each source is associated with an at least approximately conical single channel, the generatrices of which converge towards the focusing point and in which a conical central needle made of a material absorbing the gamma rays is positioned.